Display and its manufacturing method

ABSTRACT

An active matrix type display device is realized by integrally forming pixel electrodes and switching thin film transistors. The display device has a panel structure formed by a pair of substrates ( 1 ), ( 2 ) bonded to each other with a predetermined gap separating them and a liquid crystal layer ( 3 ) held in the gap between the pair of substrates. A set of thin film transistors ( 4 ), a planarizing film ( 5 ) covering said thin film transistors and a set of pixel electrodes arranged on the planarizing film ( 5 ) are formed on one of the substrates ( 1 ), whereas an opposite electrode is formed vis-a-vis the set of pixel electrodes on the other substrate ( 2 ). The planarizing film ( 5 ) of the display device is made of a photosensitive material and formed to show a varying thickness in the first substrate ( 1 ) by means of an exposure process. The parts of the planarizing film ( 5 ) that correspond to the pixel electrodes have a thickness that is made to vary according to the wavelength of the display colour assigned to each of the pixel electrodes.

TECHNICAL FIELD

[0001] This invention relates to a display device and a method ofmanufacturing the same. More particularly, the present invention relatesto an improvement to the planarizing technique that is being used forburying undulations produced by thin film transistors and their wires inthe process of manufacturing an active matrix type display device, whichcomprises as integral parts thereof pixel electrodes and switching thinfilm transistors, so as to form pixel electrodes on the planarizedsurface.

BACKGROUND ART

[0002] Conventional display devices typically have a so-called panelstructure produced by arranging a pair of substrates with apredetermined gap separating them and bonding them to each other with anelectro optic substance such as liquid crystal held in the gap. A set ofthin film transistors are formed on one of the substrates and covered bya planarizing film, on which a set of pixel electrodes are arranged,whereas an opposite electrode is arranged on the other substratevis-a-vis the set of pixel electrodes.

[0003] In the case of a colour display device, colour filters arearranged on the so-called other substrate so as to assign the threeprimary display colours of red, blue and green are to each of the pixelelectrodes. Each pixel electrode transmits or reflects light of thewavelength of the colour assigned to it in order to cause the displaydevice to display a desired colour image. The thickness of the layer ofthe electrooptic substance, which may typically be liquid crystal, ofthe colour display device needs to be regulated according to thewavelength of the colour assigned to each pixel so as to optimize thetransmission factor or the reflection factor. However, conventionalcolour display devices are not provided with such a regulating functionand hence it is difficult to optimally balance the three primary coloursof red, blue and green on the display screen.

[0004] Active matric type display devices of the built-in drive circuittype are known. The display device of this type comprises highperformance polysilicon thin film transistors to make it possible tointegrally form a pixel array section and a peripheral drive circuitsection on a same substrate. The pixel array section is formed by usingpixel electrodes and thin film transistors for driving the pixelelectrodes. The drive circuit section is also formed by using thin filmtransistors that are adapted to drive the pixel array section. The pixelarray section and the drive circuit section formed on a same substrateare covered by a common planarizing film. Since the pixel array sectionand the drive circuit section are different from each other in terms ofthe micro-structure on the surface of the substrate, it is not alwayspossible to uniformly planarize the two sections so that the thicknessof the electrooptic substance, which may typically be liquid crystal,may locally show fluctuations to consequently degrade the quality of thedisplayed image.

[0005] Additionally, in the case of reflection type display devices,micro-undulations are formed on the surface of the planarizing film andlight-reflecting pixel electrodes are formed thereon so that the pixelelectrodes may be made to provide a desired light scattering effect.However, a special processing step needs to be introduced for formingmicro-undulations on the planarizing film to complicate themanufacturing process.

DISCLOSURE OF THE INVENTION

[0006] In view of the above identified circumstances, it is thereforethe object of the present invention to provide a novel display deviceand a method of manufacturing the same that can dissolve thetechnological problems of conventional display devices.

[0007] In an aspect of the invention, the above object is achieved byproviding a display device having a panel structure formed by a pair ofsubstrates bonded to each other with a predetermined gap separating themand an electrooptic substance held in the gap between the pair ofsubstrates, a set of thin film transistors, a planarizing film coveringsaid thin film transistors and a set of pixel electrodes arranged on theplanarizing film being formed on one of the substrates, or the formersubstrate, an opposite electrode being formed vis-a-vis the set of pixelelectrodes on the other substrate, or the second substrate. Theplanarizing film of the display device is made of a photosensitivematerial and formed to show a varying thickness in the first substrateby means of an exposure process.

[0008] In a display device according to the invention, preferably thefirst substrate has thereon a pixel array section formed by the pixelelectrodes and thin film transistors for driving the pixel electrodesand a drive circuit section formed by thin film transistors for drivingthe pixel array section and the planarizing film is formed so as toextend from the pixel array section to the peripheral drive circuitsection and show a thickness differentiated between the pixel arraysection and the drive circuit section.

[0009] In a display device according to the invention, preferably theplanarizing film has a region where the thickness thereof is made tovary so as to produce undulations on the surface and the pixelelectrodes are made of reflective film and arranged in the regionshowing undulations. In a display device according to the invention,preferably, different display colours are assigned to the pixelelectrodes and the planarizing film is formed to show a thickness thatvaries according to the wavelength of the display colour assigned toeach of the pixel electrodes.

[0010] In another aspect of the present invention, there is provided amethod of manufacturing a display device having a panel structure formedby a pair of substrates bonded to each other with a predetermined gapseparating them and an electrooptic substance held in the gap betweenthe pair of substrates, the method including a step of forming a set ofthin film transistors, a planarizing film covering said thin filmtransistors and a set of pixel electrodes arranged on the planarizingfilm on one of the substrates, or the former substrate, and forming anopposite electrode vis-a-vis the set of pixel electrodes on the othersubstrate, or the second substrate, the step of forming said planarizingfilm including an application step of applying a photosensitive materialonto the first substrate, an exposure step of subjecting the planarizingfilm to an exposure process using a varied planar distribution ofquantity of exposure light and a processing step of processing theplanarizing film so as to make it show a thickness varied according tothe planar distribution of quantity of exposure light by etching thesurface of the exposed planarizing film. In a method of manufacturing adisplay device according to the invention, preferably light isirradiated onto the planarizing film by way of a mask showing a variedplanar distribution of transmission factor in the exposure step. Theplanarizing film is made to sense light for a plurality of times in theexposure step, using a plurality of masks, in order to irradiate lightto the planarizing film with a predetermined quantity of energy.Alternatively, a single mask provided with a filter having predeterminedparts adapted to irradiate light to the planarizing film with differentrespective quantities of energy may be used. A pattern adapted todiffract light may be used for the filters in the exposure step.Alternatively, a filter made of two or more than two light shieldingsubstances having different light transmission factors may be used.Preferably, a mask provided with a filter showing a light transmissionfactor between 1% and 50% is used in the exposure step.

[0011] Thus, in a display device according to the invention realized byusing an electro optic substance such as liquid crystal, the planarizingfilm applied to the surface of a substrate integrally carrying activeelements such as thin film transistors is so devised that its thicknessis made to vary within the substrate. With this arrangement, it is nowpossible to provide each of the red, blue and green pixels of the colourdisplay device with an optimal thickness. Therefore, it is possible toimprove the uneven gap in both of the pixel array section and the drivecircuit section of the panel of a built-in drive circuit type displaydevice realized by integrally forming pixel arrays and drive circuits.Additionally, in the case of a reflection type display device, it is nowpossible to make the pixel electrodes operating as reflective filmprovide a desired light scattering effect with a reduced number ofsteps, by varying the thickness of the planarizing film so as to produceundulations on the surface thereof.

[0012] The other objects and the advantages of the present inventionwill be made clear in the following description of the preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic cross sectional view of a part of a displaydevice according to the invention, illustrating its basic configuration.

[0014]FIG. 2 is a schematic cross sectional view of a part of the firstembodiment of display device according to the invention.

[0015]FIG. 3 is a graph illustrating the relationship between theexposure time and the extent of etching the planarizing film of adisplay device according to the invention.

[0016]FIG. 4 is a cross sectional view of a part of a display deviceshown for reference.

[0017]FIG. 5 is a cross sectional view of a part of a display devicealso shown for reference.

[0018]FIG. 6 is a schematic cross sectional view of a part of the secondembodiment of display device according to the invention.

[0019]FIG. 7 is a cross sectional view of a part of display device alsoshown for reference.

[0020]FIG. 8 is a schematic cross sectional view of a part of the thirdembodiment of display device according to the invention.

[0021]FIG. 9 is a schematic plan view of a cellular phone terminaldevice realized by applying the present invention.

[0022]FIG. 10 is a schematic perspective views of a portable informationterminal device realized by applying the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] Now, the present invention will be described in greater detail byreferring to the accompanying drawings that illustrate preferredembodiments of the invention.

[0024] Firstly, the general configuration of colour display devices willbe briefly described by referring to FIG. 1 in order to clarify thebackground of the invention. The display device of FIG. 1 has aso-called panel structure produced by arranging a pair of glasssubstrates 100, 135 with an electrooptic substance 130 held between thesubstrates. In FIG. 1, an opposite electrode 131, a planarizing layer132, a colour filter 133 and a black matrix 134 are formed on the upperglass substrate 135.

[0025] On the other hand, a pixel array section 120 and a drive circuitsection 130 are arranged on the lower substrate 100. The drive circuitsection 130 is located peripherally relative to the pixel array section120. The pixel array section 120 includes pixel electrodes 111 and thinfilm transistors (TFT-PXL) for switching/driving the pixel electrodes111. The thin film transistors TFT-PXL have a dual gate type bottom gatestructure and are N-channel type transistors. On the other hand, thedrive circuit section 130 includes thin film transistors (TFT-CKT) fordriving the thin film transistors TFT-PXL. In the instance of FIG. 1,they are of the single gate type and have a bottom gate structure. Notethat only an N-channel type thin film transistor TFT-CKT is shown inFIG. 1. Both the thin film transistors TFT-PXL and thin film transistorsTFT-CKT have a multilayer structure realized by sequentially laying agate electrode 101, gate insulating films 102, 103 and a semiconductorthin film 105. The semiconductor thin film 105 is typically made ofpolycrystalline silicon. The gate insulating films are a gate nitridefilm 102 and a gate oxide film 103.

[0026] The semiconductor thin film 105 is patterned to produce islandsthat correspond to the element regions of the thin film transistors. Thepatterned semiconductor thin film 105 has channel regions ch locatedinside the ends of the respective gate electrodes 101, low concentrationimpurity regions (LDD regions) extending outward from the respectivechannel regions ch and high concentration impurity regions (sourceregions S and drain regions D) extending outward from the respective lowconcentration impurity regions (LDD regions). The channel region ch ofeach thin film transistor is protected by a stopper film 106. The thinfilm transistors TFT-PXL, TFT-CKT are covered by an interlayerinsulating film 107 and a protection film 108. Wiring electrodes 109 areformed on the protection film 108. Each wiring electrode 109 iselectrically connected to the source region S or the drain region D ofthe corresponding thin film transistor by way of a contact hole formedthrough the interlayer insulating film 107 and the protection film 108.The wiring electrodes 109 are covered by a planarizing film 110. Pixelelectrodes 111 are formed on the planarizing film 110 by patterning.

[0027] As described above, the substrate 100 carrying a pixel arraysection and a drive circuit section and an opposite substrate 135carrying a colour filter 133 and an opposite electrode 131 are disposedvis-a-vis with an electrooptic substance 130 interposed between them inthe colour display device of FIG. 1. The pixels that control transmittedlight form an organic planarizing film 110 as passivation layer on thegate insulating film and the interlayer insulating film that arecomponents of the thin film transistors and the pixel electrodes 111typically made of transparent electrically conductive film such as ITOfilm are formed on the planarizing film. On the other hand, a colourfilter 133 of the three primary colours of red, blue and green and ablack matrix 134 are formed on the opposite substrate 135 side and aplanarizing layer 132 operating as overcoat layer and an oppositeelectrode 131 are formed on the colour filter 133 and the black matrix134. The liquid crystal layer sandwiched by the substrates 100, 135 havea substantially same thickness and shows the highest transmission factorin a specific wavelength zone that is defined as a function of the filmthickness and the refractive index of the liquid crystal layer. In thecase of the simple structure as illustrated in FIG. 1, the specificwavelength zone is normally so defined as to make it agree with that ofgreen colour in order to maximize the transmission factor of the panelbut with that of blue colour when the colour temperature is emphasizedat the time of displaying white. Improvement in terms of transmissionfactor and colour temperature has been required recently and it isnecessary to make the liquid crystal layer show an optimal filmthickness for all the wavelengths of red, green and blue in order tomeet the requirement. However, with the structure of FIG. 1, it isdifficult to change the film thickness of the liquid crystal layer foreach pixel without remarkably increasing the number of processing steps.

[0028]FIG. 2 is a schematic cross sectional view of a par of the secondembodiment according to the invention.

[0029] As shown in FIG. 2, this embodiment of display device has aso-called panel structure produced by arranging a pair of substrates 1,2 with an electrooptic substance such as liquid crystal 3 held betweenthe substrates. The paired upper and lower substrates 1, 2 are bonded toeach other by means of a sealing material 9 with the liquid crystal 3interposed between them. A set of thin film transistors 4 for forming apixel array section 21 and a drive circuit section 22, a planarizingfilm 5 covering the thin film transistors 4 and a set of pixelelectrodes arranged in the pixel array section 21 on the planarizingfilm 5 are disposed on one of the substrates, or the substrate 1. Notethat the pixel electrodes are not shown in FIG. 1. Wires 6 are arrangedon the set of thin film transistors 4 and the above describedplanarizing film 5 is formed so as to cover the wires 6.

[0030] The above described set of thin film transistors 4 is dividedinto the pixel array section 21 integrally comprising a plurality ofpixels PXL and the peripheral drive circuit section 22. On the otherhand, the upper substrate 2 carries the opposite electrode that isarranged vis-a-vis the set of pixel electrodes. Note that the oppositeelectrode is not shown in FIG. 2. The planarizing film 5 is made of aphotosensitive material and shaped by way of an exposure processingoperation so as to show a thickness that varies depending on the spot inthe first substrate 1.

[0031] A colour filter CF and a black matrix 7 are formed on thesubstrate 2 in addition to the opposite electrode and covered by aprotection film 8. Actually, the opposite electrode is formed on theprotection film 8. Different display colours of red (R), green (G) andblue (B) are assigned to the pixels PXL by means of the colour filterCF. The planarizing film 5 is shaped in such a way that the thickness ofits part corresponding to the pixels PXL varies as a function of thewavelength of the display colour assigned to each pixel.

[0032] Thus, the embodiment of FIG. 2 is so designed that the liquidcrystal layer 3 shows a film thickness that maximizes its transmissionfactor for light of the wavelength zone of the display colour assignedto each pixel PXL by processing the photosensitive organic planarizingfilm 5. ECB liquid crystal that is typically used for the VA mode isadopted for the liquid crystal layer 3. For example, the film thicknessof the liquid crystal layer 3 is made to vary so that it shows athickness D₁ or 3.7 μm for the parts of the red pixels, a thickness D₂of 3.5 μm for the parts of the green pixels and a thickness D₃ of 2.8 μmfor the parts of the blue pixels.

[0033] Photolithography and etching may be used in combination with amaterial for the planarizing film so that the planarizing film may showa film thickness that varies depending on the spot on the film.Generally, when manufacturing a display device having a so-called panelstructure produced by arranging a pair of substrates with anelectrooptic substance such as liquid crystal held between thesubstrates, a set of thin film transistors, a planarizing film coveringthe transistors and a set of pixel electrodes to be arranged on theplanarizing film are formed on one of the substrates, or the firstsubstrate, while an opposite electrode is formed vis-a-vis the set ofpixel electrodes on the other substrate, or the second substrate. Asdescribed above, the process of forming the planarizing film includes anapplication step of applying a photosensitive material onto the firstsubstrate, an exposure step of subjecting the planarizing film to anexposure process using a varied planar distribution of quantity ofexposure light and a processing step of processing the planarizing filmso as to make it show a thickness varied according to the planardistribution of quantity of exposure light. Preferably, light isirradiated onto the planarizing film by way of a mask showing a variedplanar distribution of transmission factor in the exposure step. Theplanarizing film is made to sense light for a plurality of times in theexposure step, using a plurality of masks, in order to irradiate lightto the planarizing film with a predetermined quantity of energy.Alternatively, a single mask provided with a filter having predeterminedparts adapted to irradiate light to the planarizing film with differentrespective quantities of energy may be used. A pattern adapted todiffract light (and hence not adapted to resolve an image) may be usedfor the filters in the exposure step. Alternatively, a filter made oftwo or more than two light shielding substances (half tone substances)having different light transmission factors may be used. Preferably, amask provided with a half tone filter showing a light transmissionfactor between 1% and 50% is used in the exposure step.

[0034] Particularly, when the planarizing film is made to show a filmthickness that varies from pixel to pixel, preferably the planarizingfilm is exposed to light to a half extent for each pixel and then thefilm thickness is reduced further by an etching operation that isconducted as a function of the extent of exposure for each pixel inorder to control the film thickness of the planarizing film. FIG. 3shows the relationship between the extent of exposure and that ofetching of the planarizing film when such a technique is used.

[0035] Referring to FIG. 3, the horizontal axis of the graph indicatesthe extent of exposure to light expressed in terms of the duration ofexposure (msec) and the vertical axis of the graph indicates the extentof etching (μm) of the planarizing film. The extent of exposure of theplanarizing film to light is controlled by using a mask that utilizes adiffraction pattern. The film thickness of the planarizing film can becontrolled by exposing it to light, using a mask, and subsequentlysubjecting it to a development process. The graph of FIG. 3 shows therelationship between the extent of exposure and that of etching of theplanarizing film for three different masks. Referring to FIG. 3, thecurve A shows the data obtained when a fully open mask is used. It willbe seen from the curve A that the extent of etching (the reduction ofthe film thickness of the planarizing film) increases as the exposuretime increases, although the extent of etching becomes saturated whenthe exposure time exceeds 500 msec. On the other hand, the curve B showsthe data obtained when a mask of a striped pattern having light zonesand dark zones arranged alternately, both the light zones and the darkzones having a width of 0.25 μm, is used. It will be seen from the curveB that the extent of etching can be controlled substantially as a linearfunction of the exposure time. Finally, the curve C shows the dataobtained when a mask of a striped pattern having light zones with awidth of 0.25 μm and dark zones with a width of 0.75 μm, said lightzones arranged alternately. Thus, the mask of the curve C blocks morelight than that of the curve B. Therefore, in the case of the curve C,while the extent of etching increases linearly proportionally relativeto the exposure time, the rate at which the extent of etching increasesis lower than that of the curve B. The above described technique ofusing a diffraction pattern for controlling the extent of exposure maybe replaced by the use of a half tone material that corresponds to apredetermined transmission factor. If such is the case, a mask isprepared by using a layer of a material whose transmission factor isknown relative to a predetermined wavelength of light to be used forexposure, MoSi for instance, and whose film thickness is so controlledas to regulate the quantity of transmitted light. For example, the filmthickness can be so controlled as to show four different values(including one for totally transmitting light) by using a three-layeredmask formed from two different half tone materials, one showing atransmission factor of 25% for red pixels and one showing a transmissionfactor of 20% or so for green pixels, and a material that completelyblock light for blue pixels.

[0036] Now, the technology that provides the background of the presentinvention will be briefly described by referring to FIG. 4 beforedescribing the second embodiment of the invention.

[0037]FIG. 4 is a cross sectional view of a part of an active matrixtype display device shown for reference. It illustrates only a pixel ofthe device. The display device has pixels arranged in the form of amatrix on a transparent substrate 201 typically made of glass. Eachpixel is divided in an open region 221 and a non-open region 222. Apixel PXL is formed in the open region 221 and adapted to emit lightthrough the substrate 201. More specifically, the pixel PXL is made ofliquid crystal 217 and held between a pair of transparent electrodes210, 219 that are arranged vis-a-vis relative to each other. It is alsoreferred to a liquid crystal cell. Note that, one of the electrodes, orthe first electrode 210, is formed at the side of the glass substrate201, while the other electrode, or the second electrode 219, is formedon an opposite substrate 220. It is also referred to as oppositeelectrode. The liquid crystal cell operates as a light bulb thatreceives light from a back light (not shown) arranged at the rearsurface side of the glass substrate 201 and emits light to the frontsurface side of the glass substrate 201. The surface of the pixelelectrode 210 is covered by an orientation film 216, while the surfaceof the opposite electrode 219 is covered by a different orientation film218.

[0038] On the other hand, a thin film transistor TFT for driving theabove described liquid crystal cell is formed in the non-open region222. As shown in FIG. 4, the thin film transistor has a bottom gatestructure and a polycrystalline semiconductor thin film 204P typicallymade of polysilicon is formed on the metal-made gate electrode 202 witha gate insulating film 203O interposed between them. The polycrystallinesemiconductor thin film 204P is covered by an interlayer insulating film207N typically made of silicon nitride and a source electrode 205S and adrain electrode 205D are formed on it. The electrodes 205S, 205D arecovered by a planarizing film 209 that is made of organic transparentresin film. The planarizing film 209 planarizes the surface of the glasssubstrate 201 and, at the same time, operates as protect film for thethin film transistor TFT. The above described pixel electrode 210 isformed in the planarizing film 209 and electrically connected to thethin film transistor TFT by way of the drain electrode 205D. The gateinsulating film 203O, the interlayer insulating film 207N and theplanarizing film 209 that are described above are laid one on the otherto produce a first film structure. The first film structure contains thethin film transistor TFT in the non-open region 222. In other words, thefirst film structure is formed to contain the thin film transistor fromthe upper and lower sides. On the other hand, a second film structureextends from the first film structure and arranged in the open-region221 that is located adjacently relative to the non-open region 222. Inthe instance of FIG. 4, the second film structure comprises only theplanarizing film 209 which is located between the liquid crystal cellformed on the pixel electrode 210 and the glass substrate 201.

[0039] In the instance of FIG. 4, all the unnecessary film is removedfrom the open region 221 and only the planarizing film 209 of organicresin is directly formed on the glass substrate 201. If the planarizingfilm 209 is made of acrylic resin, its refractive index is 1.4 to 1.6and does not practically differ from that of the glass substrate 201 atall. Therefore, no unnecessary reflection occurs along the interface dueto difference of refractive index. Thus, by removing layers showingdifferent refractive indexes from the open region 221 as much aspossible, the multilayer interference is reduced to improve thetransmission factor of the panel. Then, because of elimination ofinterference effect, variances among the products can be minimized.Additionally, reflection of the panel can also be minimized.Furthermore, since the non-open region 222 and the open region 221 canbe treated in a common process, the manufacturing process does notrequire any additional steps if compared with conventional manufacturingmethods.

[0040]FIG. 5 is a cross sectional view of a part of a display device ofFIG. 4 also shown for reference. The drive circuit section 22 is shownin FIG. 5 in addition to the pixel array section. In order to facilitateunderstanding, the parts corresponding to those of the first embodimentof the present invention illustrated in FIG. 2 are denoted respectivelyby the same reference symbols. As shown in FIG. 5, the display device isdivided into a pixel array section 21 where pixels PXL are integrallyformed and a peripheral drive circuit section 22. It will be appreciatedthat FIG. 4 shows a pixel PXL formed in the pixel array section 21 inenlarged dimensions.

[0041] Both the drive circuit section 22 and the pixel array section 21are formed on an insulating substrate 1 and include a set of thin filmtransistors 4. As seen from FIG. 5, the set of thin film transistors 4is covered by an interlayer insulating film 10 and wires 6 are formed onthe surface of the latter by means of a patterning operation. The wires6 are covered by a planarizing film 5 that extends to both the drivecircuit section and the pixel array section. A colour filter CF and ablack matrix 7 are formed on the inner surface of the upper substrate 2.The upper and lower substrates 1, 2 are bonded to each other by means ofa sealing material 9 with a liquid crystal layer 3 interposed betweenthem. Gap spacers 11 are arranged in the gap separating the substrates1, 2.

[0042] As described above by referring to FIG. 4, reflection due tointerference is reduced to improve the transmission factor and thecolour temperature of the open region 221 of each pixel PXL of the pixelarray section 21 by removing the films showing different refractiveindexes therefrom except the planarizing film 5. However, it isdifficult for the planarizing film 5 to completely eliminate the stepsproduced by the gate insulating film and the interlayer insulating film10, which may be of the size of about 0.6 μm. In other words, thesurface of the planarizing film 5 may show a remarkable step between thedrive circuit section 22 and the pixel array section 21. Therefore, aproblem of uneven gap can occur in a peripheral part of the panelparticularly when the gap spacers 11 distributed in the pixel arraysection 21 ride on the planarizing film 5 in the drive circuit section.

[0043]FIG. 6 is a schematic cross sectional view of a part of the secondembodiment of display device according to the invention, which dissolvesthe problem of the device illustrated in FIG. 5 for reference. In orderto facilitate understanding, the parts corresponding to those of thedevice illustrated in FIG. 5 are denoted respectively by the samereference symbols. As clearly shown in FIG. 6, the surface of theplanarizing film 5 is lowered to make the film 5 show a film thicknessreduced to a certain extent in the drive circuit section 22 if comparedwith the pixel array section in order to avoid an uneven gap in theperipheral area of the panel. More specifically, the thickness of theplanarizing film 5 is reduced by etching it from the surface thereof inthe peripheral drive circuit section 22, taking the thickness of theinterlayer insulating film 10 into consideration, so that theplanarizing film 5 may show a uniform surface over the entire area ofthe substrate 1. If, for instance, the planarizing film 5 is formed byapplying photosensitive organic resin to the surface of the substrate 1and subsequently subjecting it to a local exposure process by using amask showing a transmission factor of 25% so that the planarizing film 5may be removed by etching from the surface thereof only in the drivecircuit section.

[0044] Now, the technology that provides the background of the presentinvention will be briefly described again by referring to FIG. 7 beforedescribing the third embodiment of the invention.

[0045]FIG. 7 is a cross sectional view of a part of display device alsoshown for reference and comprising a pair of substrates 301, 302, or afront substrate and a rear substrate, bonded to each other with apredetermined gap separating them and a layer of an electroopticsubstance such as a liquid crystal layer 303 held in the gap. Pixels arearranged in the form of a matrix in the device and adapted to reflectlight striking it from the front surface side back to the front surfaceside. The reflecting region of the device comprises electrodes 310, 322formed respectively on the pair of substrates 301, 302, the liquidcrystal layer 303 sandwiched between the electrodes 310, 322 and areflection layer 308 formed on the rear substrate 302 and provides aso-called reflection type liquid crystal display element LC.

[0046] A planarizing layer 340 and a quarter-wave plate 309 are formedon the outer surface of the substrate 301. A colour filter CF formed bya coloured layer 350 is arranged on the inner surface of the substrate301. A black matrix BM is formed also on the inner surface of thesubstrate 301 so as to divide the colour filter CF into small units thatcorrespond to so many pixels.

[0047] An opposite electrode 310 is formed on the surface of the colourfilter CF and that of the black matrix BM to commonly correspond to thepixels. An orientation film 307 is formed on the opposite electrode 310.The liquid crystal layer 303 is arranged on the orientation film 307 andadapted to show a composite refractive property. The rear substrate 302is arranged below the liquid crystal layer 303. The surface of thesubstrate 302 is covered by an orientation film 315, which cooperateswith the orientation film 307 of the front substrate 301 to orient theliquid crystal layer 303 typically in a horizontal direction. Thereflection layer 308 is arranged under the orientation film 315 anddesigned to operate as pixel electrodes. The reflection layer 308 ismade of metal film formed on the undulated surface of the planarizingfilm 314 and designed to operate as pixel electrodes. Thin filmtransistors 308 are formed below the planarizing film 314. The thin filmtransistors 308 have a bottom gate structure, which is a multilayerstructure realized by sequentially laying a gate electrode 316, a gateinsulating film 317 and a semiconductor thin film 318. The semiconductorthin film 318 is typically made of polycrystalline silicon and protectedfrom above by a stopper 319 in a channel region that matches the gateelectrode 316. Each of the thin film transistors 308 having such abottom gate structure is covered by an interlayer insulating film 320.The interlayer insulating film 320 has a pair of contact holes and asource electrode 321 and a drain electrode 322 are electricallyconnected to the thin film transistor 308 by way of the respectivecontact holes. The electrodes 321 and 322 are typically formed bypatterning an aluminum film. The drain electrode 322 is connected to theabove described reflection layer 308. Thus, the reflection layer 308 iselectrically connected to the drain electrode 322 by way of the contacthole 312 formed in the planarizing film 314. On the other hand, a signalvoltage is applied to the source electrode 321.

[0048] With the above described reflection type display device,undulations are rondomly formed on the planarizing film 314 that isproduced by applying organic resin onto the substrate 302 in order toimprove the visibility of reflected light. However, known manufacturingmethods for manufacturing such a display device are accompanied by aproblem of productivity because two organic planarizing film layers needto be subjected to an exposure process in order to randomly formundulations. The third embodiment of the present invention is designedto avoid this problem by using a structure as shown in FIG. 8. Thepresent invention also provides a method of manufacturing a displaydevice having such a structure.

[0049] In order to facilitate understanding, only the lower substrate 1of the display device is shown in FIG. 8. A planarizing film 5 is formedon the substrate 1. Undulations 12 for reflection film and a contacthole CON are formed in the planarizing film 5. Photolithography andetching are used along with a mask M for forming the undulations 12 andthe contact hole CON. In other words, the photosensitive planarizingfilm 5 is subjected to an exposure process by using the mask M in orderto locally control the film thickness of the planarizing film 5. Morespecifically, the parts of the mask corresponding to the contact holesCON where the organic planarizing film 5 is completely removed are madeto show a transmission factor of 100% and the parts for formingundulations 12 are formed by using a half tone material 51 showing atransmission factor of 20% and a completely light shielding material 52.In other words, a film layer of the half tone material 51 and that ofthe completely light shielding material 52 are formed on the basematerial 50 of the mask M. With this arrangement, it is possible toproduce undulations 12 and contact holes 51 simultaneously. An aligneradapted to use rays of light having a long wavelength such as g rays orh rays is preferably used for the purpose of the invention. Mildundulations can easily be produced by de-focussing light in the exposureprocess. More mild undulations can be produced by heating the organicplanarizing film 5 for a re-flow process. With the above describedmethod, the process of producing undulations 12 that normally requires anumber of processing steps is greatly simplified so that a displaydevice according to the invention can be manufactured at reduced cost.

[0050] While typical bottom gate type transistors are used in the abovedescription, the present invention is by no means limited thereto andthe present invention can be applied equally to the use of other topgate type transistors, a-Si transistors and simple matrix type liquidcrystal.

[0051]FIG. 9 is a schematic plan view of a cellular phone terminaldevice realized by applying the present invention.

[0052] As shown in FIG. 9, the cellular phone terminal device 400 has acompact structure realized by forming as integral parts thereof anoperating section that is used for making a call and receiving a call, atalking section that is used for a telephone conversation after making acall or receiving a call and a display section that can displayinformation relating at least to the operation for the call. Morespecifically, the cellular phone terminal device 400 comprises anantenna 431 for radio transmission/reception, a receiver 432 and atransmitter 433 along with operation keys 434 including dial keys and adisplay section 435. The receiver 432 comprises a loudspeaker and thetransmitter 433 comprises a microphone.

[0053] The display section 435 of the cellular phone terminal device 400comprises a display device according to the invention. The cellularphone terminal device 400 can display telephone direction informationincluding personal names and telephone numbers on the display section435. If desired, it may be so designed that it can display the receivede-mails on the display section 435.

[0054]FIG. 10 is a schematic perspective views of a portable informationterminal device realized by applying the present invention.

[0055] Referring to FIG. 10, the portable information terminal device(PDA) 500 has a compact structure realized by forming as integral partsthereof an operating section 511 that is used for inputtinginstructions, a processing section 510 that is used for processinginformation according to instructions and a display section S20 that candisplay processed information. The processing section 510 comprises acommunication section, a sound processing section, a control section anda memory section that are necessary for performing basic functions of aPDA. The control section that typically comprises a CPU controls thesefunctions to allow the information terminal device to operate astelephone set or as personal computer for sending/receiving e-mails,communicating with other personal computers and/or controlling personalinformation. Any of the above functions can be selected by operating theoperating section 511. The processing section 510 generates imageinformation according to the processing operation it performs. Thedisplay section 520 displays the image information generated by theinformation processing section 510.

[0056] The display section 520 may be a colour display device, areflection type display device or a display device having a built-indrive circuit realized by applying the present invention.

Industrial Applicability

[0057] Thus, according to the invention, it is now possible to form aphotosensitive organic planarizing film having a varied film thicknesson a same substrate by preparing a pattern for transmitting variedquantity of light in a same mask to be used for exposure to light. Then,a multi-gap panel can be formed for RGB pixels to improve thetransmission factor and the colour reproducibility. Additionally, it ispossible to improve the uneven gap and hence the quantity of thedisplayed image by reducing the film thickness of the organicplanarizing film on the peripheral drive circuit section. Furthermore,it is now possible to prepare undulations and contact holes of areflection type display device in a same step to reduce the number ofsteps and hence the overall manufacturing cost.

1. A display device having a panel structure formed by a pair ofsubstrates bonded to each other with a predetermined gap separating themand an electrooptic substance held in the gap between the pair ofsubstrates; a set of thin film transistors, a planarizing film coveringsaid thin film transistors and a set of pixel electrodes arranged on theplanarizing film being formed on one of the substrates, or the formersubstrate; an opposite electrode being formed vis-a-vis the set of pixelelectrodes on the other substrate, or the second substrate; and theplanarizing film of the display device being made of a photosensitivematerial and formed to show a varying thickness in the first substrateby means of an exposure process.
 2. The device according to claim 1,wherein said first substrate has thereon a pixel array section formed bythe pixel electrodes and thin film transistors for driving the pixelelectrodes and a drive circuit section formed by thin film transistorsfor driving the pixel array section, and said planarizing film is formedso as to extend from the pixel array section to the peripheral drivecircuit section and show a thickness differentiated between the pixelarray section and the drive circuit section.
 3. The device according toclaim 1, wherein said planarizing film has a region where the thicknessthereof is made to vary so as to produce undulations on the surface andthe pixel electrodes are made of reflective film and arranged in theregion showing undulations.
 4. The device according to claim 1, whereindifferent display colours are assigned to the pixel electrodes and theplanarizing film is formed to show a thickness that varies according tothe wavelength of the display colour assigned to each of the pixelelectrodes.
 5. A method of manufacturing a display device having a panelstructure formed by a pair of substrates bonded to each other with apredetermined gap separating them and an electrooptic substance held inthe gap between the pair of substrates, said method including: a step offorming a set of thin film transistors, a planarizing film covering saidthin film transistors and a set of pixel electrodes arranged on theplanarizing film on one of the substrates, or the former substrate, andforming an opposite electrode vis-a-vis the set of pixel electrodes onthe other substrate, or the second substrate; said step of forming saidplanarizing film including: an application step of applying aphotosensitive material onto the first substrate; an exposure step ofsubjecting the planarizing film to an exposure process using a variedplanar distribution of quantity of exposure light; and a processing stepof processing the planarizing film so as to make it show a thicknessvaried according to the planar distribution of quantity of exposurelight, by etching the surface of the exposed planarizing film.
 6. Themethod according to claim 5, wherein light is irradiated onto theplanarizing film by way of a mask showing a varied planar distributionof transmission factor in the exposure step.
 7. The method according toclaim 5, wherein the planarizing film is made to sense light for aplurality of times in the exposure step, using a plurality of masks, inorder to irradiate light to the planarizing film with a predeterminedquantity of energy.
 8. The method according to claim 6, wherein a singlemask provided with a filter having predetermined parts adapted toirradiate light to the planarizing film with different respectivequantities of energy is used in said exposure step.
 9. The methodaccording to claim 8, wherein a pattern adapted to diffract light may beused for the filters in the exposure step.
 10. The method according toclaim 8, wherein a filter made of two or more than two light shieldingsubstances having different light transmission factors is used in theexposure step.
 11. The method according to claim 8, wherein a maskprovided with a filter showing a light transmission factor between 1%and 50% is used in the exposure step.
 12. The method according to claim5, wherein a pixel array section comprising pixel electrodes and thinfilm transistors for driving the pixel electrodes and a drive circuitsection comprising thin film transistors for driving the pixel arraysection are formed on one of said substrates; and said planarizing filmis formed to extend from the pixel array section to the peripheral drivecircuit section and have a film thickness differentiated between thepixel array section and the drive circuit section.
 13. The methodaccording to claim 5, wherein a region having surface undulations with avaried thickness is formed in said planarizing film and the pixelelectrodes are made of reflective film and arranged in the region havingsurface undulations.
 14. The method according to claim 5, whereindifferent display colours are assigned to the pixel electrodes and thethickness of the parts of said planarizing film corresponding to thepixel electrodes are made to vary according to the wavelengths of thedisplay colours assigned to the respective pixel electrodes.
 15. Acellular phone terminal device comprising an operating section to beused for operations relating to making a call and receiving a call, atalking section to be used for allowing telephone conversation to takeplace after making a call or receiving a call and a display section fordisplaying information relating at least to the operation for the call;said display section having a panel structure formed by a pair ofsubstrates bonded to each other with a predetermined gap separating themand an electro optic substance held in the gap between the pair ofsubstrates; a set of thin film transistors, a planarizing film coveringsaid thin film transistors and a set of pixel electrodes arranged on theplanarizing film being formed on one of the substrates, or the formersubstrate; an opposite electrode being formed vis-a-vis the set of pixelelectrodes on the other substrate, or the second substrate; and theplanarizing film of the display device being made of a photosensitivematerial and formed to show a varying thickness in the first substrateby means of an exposure process.
 16. The device according to claim 15,wherein said first substrate has thereon a pixel array section formed bythe pixel electrodes and thin film transistors for driving the pixelelectrodes and a drive circuit section formed by thin film transistorsfor driving the pixel array section, and said planarizing film is formedso as to extend from the pixel array section to the peripheral drivecircuit section and show a thickness differentiated between the pixelarray section and the drive circuit section.
 17. The device according toclaim 15, wherein said planarizing film has a region where the thicknessthereof is made to vary so as to produce undulations on the surface andthe pixel electrodes are made of reflective film and arranged in theregion showing undulations.
 18. The device according to claim 15,wherein different display colours are assigned to the pixel electrodesand the planarizing film is formed to show a thickness that variesaccording to the wavelength of the display colour assigned to each ofthe pixel electrodes.
 19. A portable information terminal devicecomprising an operating section to be used for inputting instructions, aprocessing section to be used for processing information according toinstructions and a display section for displaying processed information;said display section having a panel structure formed by a pair ofsubstrates bonded to each other with a predetermined gap separating themand an electrooptic substance held in the gap between the pair ofsubstrates; a set of thin film transistors, a planarizing film coveringsaid thin film transistors and a set of pixel electrodes arranged on theplanarizing film being formed on one of the substrates, or the formersubstrate; an opposite electrode being formed vis-a-vis the set of pixelelectrodes on the other substrate, or the second substrate; and theplanarizing film of the display device being made of a photosensitivematerial and formed to show a varying thickness in the first substrateby means of an exposure process.
 20. The device according to claim 19,wherein said first substrate has thereon a pixel array section formed bythe pixel electrodes and thin film transistors for driving the pixelelectrodes and a drive circuit section formed by thin film transistorsfor driving the pixel array section, and said planarizing film is formedso as to extend from the pixel array section to the peripheral drivecircuit section and show a thickness differentiated between the pixelarray section and the drive circuit section.
 21. The device according toclaim 19, wherein said planarizing film has a region where the thicknessthereof is made to vary so as to produce undulations on the surface andthe pixel electrodes are made of reflective film and arranged in theregion showing undulations.
 22. The device according to claim 19,wherein different display colours are assigned to the pixel electrodesand the planarizing film is formed to show a thickness that variesaccording to the wavelength of the display colour assigned to each ofthe pixel electrodes.